The present invention pertains to a method and apparatus for producing detergent bars having a marbled appearance. As used herein the term "detergent" is meant to include fatty acid soaps, synthetic detergents or combinations of these materials. "Detergent bars" are defined as milled and plodded toilet bars with or without emollients and/or bacteriostats made from "detergent" materials.
The prior art is replete with what is commonly known as variegated or striated bar made either as a framed soap or a milled and plodded bar. Mild and plodded toilet bars having a variegated or striated appearance are known from U.S. Pat. Nos. 3,485,905 and 3,673,294 among others. The toilet bars of the invention are clearly distinguishable over the variegated or striated bars of the prior art by having a pattern of colored detergent against a contrasting base that can be accurately described as "marbleized" since it includes wavy veining and mottling with spots and blotches as opposed to the typical striations or longitudinal streaks of the prior art. The new bars are further characterized by clear and distinct lines of demarcation between the base and contrasting components; and a minimum of bleeding or smearing of the colored component into the base.
In producing multicolored bars from milled and plodded detergents a significant problem encountered is smearing of the colored substance into the base component during mixing by the plodder worm and extrusion through the apertures of a pressure plate. The base component of the bar is typically a white soap which is discolored by the smearing and as a result presents less of a contrasting background for the colored component. For example, if it were desired to produce a multicolored bar having a white background with deep green striations or mottling, excessive mixing of the colored material, either in the form of a liquid dye or pigment dispersion, with the white base component by the plodder screw could result in an extruded billet having a light green background with medium green striations or mottled areas.
A primary advantage of the invention is to provide a method and apparatus for producing multicolored toilet bars from milled and plodded detergents wherein the colored pattern is distinct, has a marbled appearance as defined above and maintains its physical integrity during use.
A further advantage of the invention is to minimize the smearing of the colored component into the base component during mixing of the combined base detergent and colored component.